1. Field of the Invention
This invention relates to a regenerative air cycle heat pump and refrigeration system in which identical components are used, the components being switched from one mode to the other by simultaneous switching of a plurality of two-way valves. More specifically, this invention uses air as both a heating and cooling medium for a load. The air refrigerant may be used directly to heat or cool the load, or a recirculation fluid such as water may be used in heat transfer relationship with the heated or cooled air.
2. Description of the Prior Art
The term "heat pump" is another name for "refrigeration machine". All refrigeration machines take heat from a low temperature source and deliver it to a higher temperature sink. The quantity of the heat given off at the higher temperature sink is always exactly equal to the heat removed from the low temperature source, plus the heat equivalent of the power input to run the refrigeration machine. Thus, all refrigeration machines, whether Freon, air cycle, Sterling cycle, Brayton cycle, etc., reject more heat at their higher temperature sink than the heat equivalent of their input power. When any refrigeration machine is used to cool outside air in the winter and reject this heat inside a building, the heat rejected in the building must be greater than the heat equivalent of the power it takes to run the machine. This increment of heat is "free" from a fuel consumption point of view.
The air cycle heat pump is an alternate to the well known Freon heat pump primarily because the Freon heat pump has several disadvantages which are serious enough to prevent its general use. First, in the Freon heat pump heat is absorbed from the ambient by heat transfer, with the cold surface of necessity colder than ambient. When the weather becomes cold, ice forms on the cold heat transfer surface of the Freon evaporator. The ice creates problems not present with the air cycle, because the presently disclosed open air cycle heat pump does not reject its heat through a heat transfer surface. Second, as the weather gets colder, the available heat capacity of a Freon heat pump decreases, while the requirement for heat obviously increases. The presently disclosed air cycle heat pump has relatively constant heating capacity as the weather gets colder. Third, buildings are normally heated with air or water supplied at a temperature of about 150.degree. F. (66.degree. C.). On a day with a temperature of 30.degree. F. -1.degree. C.), which is average winter weather over most of the United States and Europe, this requires an evaporator temperature of about 0.degree. F. (-18.degree. C.) and a condensor for the Freon heat pump at a temperature of about 160.degree. F. (71.degree. C.). This in turn requires a Freon compressor pressure ratio of about 25 to 1. The disclosed air cycle heat pump on a similar day provides about 150.degree. F. (66.degree. C.) air for heating with a compressor pressure ratio of less than 2 to 1, so that a much simpler aerodynamic compressor may be used rather than a high pressure ratio positive displacement compressor. Fourth, Freon leakage contributes to high initial cost and high maintenance cost for Freon heat pumps. Air cycle heat pumps may leak also, but air leaks are of little consequence.
Prior art air cycle heat pumps suffer both from lack of efficiency and from problems caused by icing. The present invention overcomes both of these problems by virtue of the novel use of a regenerative heat exchanger upstream of the cooling turbine to reduce turbine inlet temperature close to the heat source temperature, combined with the turbine discharge air being discharged to ambient at a temperature far below heat source temperature. This novel construction maximizes the free heat and minimizes ice problems by directly rejecting the turbine discharge air into the ambient in the heat pump mode, whereas prior art systems cool the ambient air by passing it through a cold heat exchanger which is not required in the present disclosure, the cold heat exchanger often becoming clogged with ice. Further, by virtue of the novel construction including switchable two-way valves, the same components may be used for both the heat pump and refrigeration modes.
It is therefore an object of this invention to provide an air cycle heat pumping and refrigeration system in which the adverse effects of moisture in the refrigerant air are minimized.
Another object of this invention is to provide the maximum possible thermodynamic cycle efficiency for air cycle heat pumping and refrigeration by virtue of the appropriate use of a regenerative heat exchanger.
Another object of this invention is a regenerative air cycle heat pump and refrigeration system utilizing the same components for both the heat pump and refrigeration modes.
A further object of this invention is the use of a plurality of two-way air valves which are simultaneously operated to switch the air cycle system between heat pump and refrigeration modes.